Driving support apparatus

ABSTRACT

A driving support apparatus for an own vehicle includes a travel trajectory obtaining unit configured to obtain a preceding vehicle trajectory which is a travel trajectory of a preceding vehicle, and a control unit configured to perform a follow-up steering control for changing a steering angle of the own vehicle in such a manner that the vehicle travels along a target traveling line determined based on the preceding vehicle trajectory. The control unit is configured to, when a first distance condition and a manual steering condition are both satisfied while the follow-up steering control is being performed, stop the follow-up steering control.

BACKGROUND 1. Technical Field

The present disclosure relates to a driving support apparatus configuredto perform a follow-up steering control for changing a steering angle ofa vehicle (own vehicle) in such a manner that the vehicle travels alonga target traveling line set based on a travel trajectory of a precedingvehicle.

2. Description of the Related Art

One of driving support apparatuses which are conventionally known isconfigured to perform a control for adjusting an acceleration (includinga deceleration) of an own vehicle in such a manner that a distancebetween the own vehicle and another vehicle (preceding vehicle)traveling in a front area of the own vehicle is maintained at apredetermined target inter-vehicle distance (for example, see JapanesePatent Application Laid-Open (kokai) 2016-101783 A). The above-mentionedcontrol is also referred to as a “following-travelinter-vehicle-distance control” or “inter-vehicle-distance control”.

Another driving support apparatus (hereinafter, referred to as a“related-art apparatus”) specifies a preceding vehicle traveling aheadof the own vehicle while the following-travel inter-vehicle-distancecontrol is being performed. Further, the related-art apparatus performsa steering control in such a manner that the own vehicle travels along atravel trajectory/locus of the specified preceding vehicle (for example,see Japanese Unexamined Patent Application Publication (Translation ofPCT Application) No. 2011-514580). The above-mentioned control is alsoreferred to as a “follow-up steering control” or“preceding-vehicle-following steering control”. Hereinafter, the traveltrajectory/locus of the preceding vehicle will be referred to as a“preceding vehicle trajectory”.

However, when performing the follow-up steering control by utilizing thepreceding vehicle trajectory, the following problem may occur. Forexample, the preceding vehicle may sometimes travel at a position awayfrom a center line of a road (travel lane). In an example of FIG. 6, apreceding vehicle 101 travels in a vicinity of a left edge 611 of atravel lane 610. In this case, the related-art apparatus performs thefollow-up steering control for the own vehicle 100 in such a manner thatthe own vehicle 100 follow a preceding vehicle trajectory L1 of thepreceding vehicle 101. Therefore, the own vehicle 100 travels in thevicinity of the left edge 611 of the travel lane 610.

In such a situation, the driver may wish to modify the position of theown vehicle 100 to a position (100*) near a center line LM of the travellane 610, and therefore, the driver may manually perform a steeringoperation (that is, manually operates a steering wheel). By thissteering operation, as illustrated by the arrow A in FIG. 6, theposition of the own vehicle 100 is moved in the road-width direction.

However, as the driver stops the manual steering operation, therelated-art apparatus performs the follow-up steering control based onthe preceding vehicle trajectory to thereby return the own vehicle 100to a position near the left edge 611 of the travel lane 610 asillustrated by the arrow B. That is, under performance of the follow-upsteering control, even if the driver intentionally performs the steeringoperation to modify the position of the own vehicle 100, the modifiedposition of the own vehicle 100 cannot be maintained. Therefore, thereis a problem that the driver feels discomfort.

SUMMARY

One or more embodiments have been devised in view of the above-mentionedproblem. Specifically, there is provided a driving support apparatusconfigured to, when the driver performs the steering operation while thefollow-up steering control is being performed, maintain the position inthe road-width direction of the own vehicle after that steeringoperation.

According to one embodiment, there is provided a driving supportapparatus for a vehicle, including:

a steering operation unit (SW) configured to be operated by a driver ofthe vehicle;

a steering device (40, 41, 42) configured to change a steering angle ofthe vehicle in response to an operation amount of the steering operationunit;

a travel trajectory obtaining unit (10, 10 b) configured to obtain apreceding vehicle trajectory which is a travel trajectory of a precedingvehicle traveling ahead of the vehicle; and

a control unit (10, 10 c) configured to perform a follow-up steeringcontrol for changing the steering angle of the vehicle in such a mannerthat the vehicle travels along a target traveling line determined basedon the preceding vehicle trajectory.

Further, the control unit is configured to, when a first distancecondition and a manual steering condition are both satisfied while thefollow-up steering control is being performed, stop the follow-upsteering control (Step 1045:Yes, Step 1050:Yes, and Step 1055). Thefirst distance condition is a condition satisfied when a deviationdistance (dv) in a road-width direction between the preceding vehicletrajectory and the vehicle is equal to or longer than a predeterminedfirst threshold (Th1). The manual steering condition is a conditionsatisfied when the driver operates the steering operation unit to changea position in the road-width direction of the vehicle.

The driving support apparatus stops the follow-up steering control, whenthe driver intentionally and manually performs the steering operation tomodify/change the position in the road-width direction of the ownvehicle while the follow-up steering control is being performed inaccordance with the target traveling line determined based on thepreceding vehicle trajectory. Therefore, the position of the own vehicle100 is not returned to the position before that modification by thefollow-up steering control based on the preceding vehicle trajectory. Inother words, the driving support apparatus can maintain the position ofthe own vehicle which has been modified/changed through the steeringoperation of the driver during performance of the follow-up steeringcontrol.

In an aspect of the driving support apparatus, the control unit isconfigured to, when a second distance condition is satisfied in a statein which the follow-up steering control is stopped owing to thesatisfaction of both the first distance condition and the manualsteering condition, resume the follow-up steering control (Step 1040:No,Step 1060:Yes, Step 1065 and Step 1070). The second distance conditionis a condition satisfied when the deviation distance is equal to orshorter than a predetermined second threshold.

According to the above aspect, in the state in which the follow-upsteering control based on the preceding vehicle trajectory is stopped,the follow-up steering control is resumed in response to the positionalrelationship between the vehicle and the preceding vehicle trajectory.For example, when the preceding vehicle moves in such a manner that thedistance between the preceding vehicle trajectory and the vehiclebecomes shorter, or the driver intentionally performs the steeringoperation to bring the position of the own vehicle to a position closeto the preceding vehicle trajectory, the driving support apparatusaccording to the present aspect can resume the follow-up steeringcontrol based on the preceding vehicle trajectory.

An aspect of the driving support apparatus further includes a detector(13, 14) configured to detect a steering-related amount (θ, Tra) whichis an amount concerning an operation state of the steering operationunit. Further, the control unit is configured to determine whether ornot the manual steering condition is satisfied based on the detectedsteering-related amount.

The driving support apparatus according to the above aspect candetermine whether or not the driver performs the steering operationbased on the steering-related amount detected by the detector.

In the above description, in order to facilitate understanding of theabove one or more aspect of the embodiment, a name and/or referencenumeral used in embodiments described below is enclosed in parenthesesand assigned to each of the constituent features corresponding to theembodiments. However, each of the constituent features is not limited tothe embodiments defined by the name and/or reference numeral.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic configuration diagram for illustrating a drivingsupport apparatus for a vehicle according to an embodiment.

FIG. 2 is a plan view for illustrating a situation in which a firstaspect of a lane keeping assist control (LTC) is performed by using atarget traveling line determined based on a preceding vehicletrajectory.

FIG. 3A is a plan view for explaining the lane keeping assist control ofFIG. 2 in more detail.

FIG. 3B shows expressions for explaining a relationship betweencoefficients of a cubic function of the preceding vehicle trajectory, acurvature of the cubic function, a radius of curvature of the cubicfunction, and the like.

FIG. 3C shows expressions for explaining a relationship between thecoefficients of the cubic function of the preceding vehicle trajectory,the curvature of the cubic function, a yaw angle, and the like.

FIG. 4 is a plan view for illustrating a situation in which a secondaspect of the lane keeping assist control (LTC) is performed by using atarget traveling line determined based on a center line of a travellane.

FIG. 5 is a diagram for illustrating a process for correcting/modifyingthe preceding vehicle trajectory based on the center line of the travellane.

FIG. 6 is a plan view for illustrating a situation in which an ownvehicle and a preceding vehicle travel in a vicinity of a left edge of atravel lane.

FIG. 7 is a plan view for illustrating a situation in which the ownvehicle is brought close to a center line of the travel lane by asteering operation of a driver of the own vehicle after the situation ofFIG. 6.

FIG. 8 is a plan view for illustrating a situation in which thepreceding vehicle travels in the vicinity of the center line of thetravel lane after the situation of FIG. 7.

FIG. 9 is a plan view for illustrating a situation in which the ownvehicle is brought close to the left edge of the travel lane after thesituation of FIG. 7.

FIG. 10 is a flowchart for illustrating one routine of the lane keepingassist control (LTC) executed by a driving support ECU according to theembodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Now, referring to the accompanying drawings, a description is given ofembodiment(s). The accompanying drawings are illustrations of one ormore specific embodiments in conformity with the principle thereof, butthose illustrations are examples to be used for the understanding of theembodiment(s), and are not to be used to limit the interpretation of thepresent disclosure.

<Configuration>

A driving support apparatus (hereinafter, referred to as an “embodimentapparatus”) according to an embodiment of the present disclosure isapplied to a vehicle. As illustrated in FIG. 1, the embodiment apparatusincludes a driving support (assist) ECU 10, an engine ECU 20, a brakeECU 30, and a steering ECU 40.

Those ECUs are electric control units each including a microcomputer asa main part, and are connected to one another so as to be able tomutually transmit and receive information via a controller area network(CAN) (not shown). The microcomputer herein includes a CPU, a RAM, aROM, an interface I/F, and the like. For example, the driving supportECU 10 includes a microcomputer including a CPU 10 v, a RAM 10 w, a ROM10 x, an interface (I/F) 10 y, and the like. The CPU 10 v executesinstructions (programs and routines) stored in the ROM 10 x to realizevarious functions.

The driving support ECU 10 is electrically connected to sensorsincluding switches described later and receives detection signals oroutput signals of the sensors, respectively. The sensors may beelectrically connected to any of the ECUs other than the driving supportECU 10. In this case, the driving support ECU 10 receives the detectionsignals or the output signals of the sensors from the ECUs electricallyconnected to the sensors via the CAN.

An acceleration pedal operation amount sensor 11 detects an operationamount (accelerator opening) AP of an acceleration pedal 11 a of the ownvehicle and outputs a detection signal or an output signal indicative ofthe operation amount AP to the driving support ECU 10. A brake pedaloperation amount sensor 12 detects an operation amount BP of a brakepedal 12 a of the own vehicle and outputs a detection signal or anoutput signal indicative of the operation amount BP to the drivingsupport ECU 10.

A steering wheel SW is a steering operation unit which is operated bythe driver for changing a steering angle of the own vehicle. The drivercan change the steering angle of the own vehicle in response to anoperation amount of the steering wheel SW.

A steering angle sensor 13 detects a steering angle θ of the own vehicleand outputs a detection signal or an output signal indicative of thesteering angle θ to the driving support ECU 10. The value of thesteering angle θ becomes a positive value when the steering wheel SW isrotated from a predetermined reference position in a first direction.The value of the steering angle θ becomes a negative value when thesteering wheel SW is rotated from the predetermined reference positionin a second direction opposite to the first direction.

A steering torque sensor 14 detects a steering torque Tra applied to asteering shaft US of the own vehicle by an operation of a steering wheelSW and outputs a detection signal or an output signal indicative of thesteering torque Tra to the driving support ECU 10. The value of thesteering torque Tra becomes a positive value when the steering wheel SWis rotated in the first direction. The value of the steering angle θbecomes a negative value when the steering wheel SW is rotated in thesecond direction.

In addition, the steering angle θ and the steering torque Tra are alsoreferred to as a “steering-related amount” for convenience.

A vehicle speed sensor 15 detects a traveling speed SPD of the ownvehicle and outputs a detection signal or an output signal indicative ofthe traveling speed SPD to the driving support ECU 10.

An ambient sensor 16 acquires at least information on a road ahead ofthe own vehicle and information on three-dimensional objects beingpresent on the road. The three-dimensional objects include, for example,moving objects such as pedestrians, bicycles, vehicles and the like, andmotionless objects such as power poles, trees, guardrails and the like.Hereinafter, the three-dimensional object will be referred to as a“target object”. The ambient sensor 16 includes a radar sensor 16 a anda camera sensor 16 b.

The radar sensor 16 a transmits radio waves each having a millimeterwave band to an area surrounding the own vehicle including at least anarea in front of the own vehicle, and receives radio waves reflected bythe target object(s) being present within a radiation range.Hereinafter, the radio wave having the millimeter wave band will bereferred to as a “millimeter wave” and the radio wave reflected by thetarget object will be referred to as a “reflected wave”. The radarsensor 16 a determines the presence or absence of the target object,calculates parameters representing a relative relationship between theown vehicle and the target object, and outputs the determination resultsand the calculation results to the driving support ECU 10. Theparameters representing the relative relationship between the ownvehicle and the target object include a position of the target objectwith respect to the own vehicle, a distance between the own vehicle andthe target object, a relative speed of the target object with respect tothe own vehicle, and the like.

Specifically, the radar sensor 16 a includes a millimeter wavetransmitting/receiving part (not shown) and a signal processing part(not shown). The signal processing part acquires, every time a certainperiod of time elapses, the parameters representing the relativerelationship between the own vehicle and the target object based on aphase difference between the millimeter wave transmitted from themillimeter wave transmitting/receiving part and the reflected wavereceived by the millimeter wave transmitting/receiving part, a dampinglevel of the received reflected wave with respect to the transmittedmillimeter wave, a time from the transmission of the millimeter wave tothe reception of the reflected wave and the like. The parameters includean inter-vehicle distance (i.e. a longitudinal distance) Dfx(n) of thedetected target object(n), a relative vehicle speed Vfx(n) of the targetobject (n), a lateral distance Dfy(n) of the target object (n), arelative lateral speed Vfy(n) of the target object (n) and the like.

The inter-vehicle distance Dfx(n) is a distance between the own vehicleand the target object (n) (e.g., a preceding vehicle) along a centralaxis of the own vehicle (central axis extending in the front-reardirection of the own vehicle, that is, the x-axis described later).

The relative vehicle speed Vfx(n) is a difference between a speed Vs ofthe target object (n) (preceding vehicle) and a speed Vj of the ownvehicle (that is, Vfx(n)=Vs−Vj). The speed Vs of the target object (n)is a speed of the target object (n) in the traveling direction of theown vehicle (that is, the x-axis described later).

The lateral distance Dfy(n) is a distance in a direction (that is, they-axis described later) perpendicular to the central axis of the ownvehicle between a central position of the target object (n) (e.g., acentral position in the vehicle-width direction of the precedingvehicle) and the central axis of the own vehicle. Hereinafter, thelateral distance Dfy(n) will be referred to as a “lateral position”.

The relative lateral speed Vfy(n) is a speed of the central position ofthe target object (n) (e.g., central position in the vehicle-widthdirection of the preceding vehicle) in the direction (that is, they-axis described later) perpendicular to the central axis of the ownvehicle.

The camera sensor 16 b includes a stereo camera (now shown) and an imageprocessing part (not shown). The stereo camera takes a pair of right andleft images of landscapes at a right side of the own vehicle ahead of(in front of) the own vehicle and at a left side of the own vehicleahead of (in front of) the own vehicle. Based on the pair of right andleft images, the image processing part determines the presence orabsence of the target object, calculates the parameters representing therelative relationship between the own vehicle and the target object, andoutputs the determination results and the calculation results to thedriving support ECU 10. In this configuration, the driving support ECU10 obtains/determines/defines the parameters representing the relativerelationship between the own vehicle and the target object bysynthesizing the following (i) and (ii):

(i) the parameters acquired by the radar sensor 16 a, which representthe relative relationship between the own vehicle and the target object,and

(ii) the parameters acquired by the camera sensor 16 b, which representthe relative relationship between the own vehicle and the target object.

The camera sensor 16 b recognizes right and left lane lines of the road(that is, a lane in which the own vehicle is traveling) based on thepair of right and left images. The camera sensor 16 b calculates a shapeof the road and a positional relationship between the road and the ownvehicle (e.g., a distance between the central position in thevehicle-width direction of the own vehicle and a left or right edge ofthe lane), and outputs the calculation results to the driving supportECU 10. The lane line includes a white line, a yellow line and the like.Hereinafter, an example where the lane line is the white line will bedescribed.

Information on the target object which is acquired by the ambient sensor16 will be referred to as “target object information”. The informationincludes the parameters representing the relative relationship betweenthe own vehicle and the target object. The ambient sensor 16 repeatedlytransmits the target object information to the driving support ECU 10every time a certain sampling period of time elapses. The ambient sensor16 does not necessarily include both the radar sensor and the camera,but may include only one of the radar sensor and the camera.

An operation switch 17 is a switch which is operated by a driver of theown vehicle. The driver can control whether or not to perform thefollowing-travel inter-vehicle-distance control such as an adaptivecruise control (ACC) described later through operating the operationswitch 17. Further, the driver can control whether or not to perform alane keeping assist control described later using the operation switch17.

A yaw rate sensor 18 detects a yaw rate YRt of the own vehicle andoutputs a detection signal or output signal indicative of the yaw rateYRt to the driving support ECU 10.

The engine ECU 20 is electrically connected to engine actuators 21 ofthe engine 22. The engine actuators 21 include at least a throttle valveactuator (not shown) for changing an opening degree of the throttlevalve of the engine 22. The engine ECU 20 can change an engine torquegenerated by the engine 22 by controlling activations of the engineactuators 21. The engine torque generated by the engine 22 istransmitted to drive wheels (not shown) through a transmission (notshown). Therefore, the engine ECU 20 can control a driving forcesupplied to the own vehicle (that is, to the drive wheels) bycontrolling the activations of the engine actuators 21 to thereby changean acceleration or an acceleration state. In the case where the ownvehicle is a hybrid vehicle, the engine ECU 20 can control the drivingforce generated by one or both of “the engine and an electric motor” asthe vehicle driving source. In the case where the own vehicle is anelectric vehicle (battery vehicle), the engine ECU 20 can control thedriving force generated by the electric motor as the vehicle drivingsource.

The brake ECU 30 is electrically connected to a brake actuator 31. Thebrake actuator 31 is provided in a hydraulic circuit provided between amaster cylinder (not shown) for pressurizing hydraulic oil by adepression force of the brake pedal 12 a and a friction brake mechanism32 provided in right and left front and rear wheels of the own vehicle.The brake actuator 31 adjusts a hydraulic pressure supplied to a wheelcylinder (not shown) in each brake caliper 32 b of the friction brakemechanism 32, depending on a command sent from the brake ECU 30. Thewheel cylinder is activated by the hydraulic pressure to press a brakepad (not shown) on the brake disc 32 a, thereby to generate a frictionbraking force on the brake disc 32 a. Therefore, the brake ECU 30 cancontrol an activation of the brake actuator 31 to control the brakingforce applied to the own vehicle (that is, to the wheels) to therebychange an acceleration or an acceleration state (or deceleration, thatis, negative acceleration).

The steering ECU 40 is a control device of a known electric poweredsteering system and is electrically connected to a motor driver 41. Themotor driver 41 is electrically connected to a steering motor 42. Thesteering motor 42 is assembled in a steering mechanism (not shown)including the steering wheel SW, the steering shaft US connected to thesteering wheel SW, a steering gear mechanism (not shown) and the like.The steering motor 42 generates a torque by an electric power suppliedfrom the motor driver 41 and uses the torque to apply a steering assisttorque to the steering shaft US to thereby steer the right and leftsteered wheels. That is, the steering motor 42 can change a steeringangle of the own vehicle.

<Control as Prerequisite of Embodiment Apparatus>

Next, an outline of controls performed by the embodiment apparatus willbe described. The driving support ECU 10 is capable of performing the“following-travel inter-vehicle-distance control such as the adaptivecruise control (ACC)” and the “lane keeping assist control”.

<Adaptive Cruise Control (ACC)>

When a preceding vehicle (referred to as an “ACC-target vehicle”) whichis traveling at a front area of the own vehicle and immediately ahead ofthe own vehicle is present, the following-travel inter-vehicle-distancecontrol has the own vehicle follow the preceding vehicle whilemaintaining an inter-vehicle distance between the preceding vehicle andthe own vehicle at a predetermined distance, based on the target objectinformation. Hereinafter, the following-travel inter-vehicle-distancecontrol will be referred to as “Adaptive Cruise Control (ACC)”. The ACCitself is widely known (e.g., refer to Japanese Patent ApplicationLaid-open No. 2014-148293, Japanese Patent Application Laid-open No.2006-315491, Japanese Patent No. 4172434, and Japanese Patent No.4929777). Thus, a brief description on the ACC is now given.

The driving support ECU 10 is configured to perform the ACC when the ACCis requested through the operation applied to the operation switch 17.

Specifically, the driving support ECU 10 selects the ACC-target vehicle,which the own vehicle should follow, based on the target objectinformation acquired by the ambient sensor 16 when the ACC is requested.For example, the driving support ECU 10 determines whether or not arelative position of the target object (n) is present within afollowing-target vehicle area. The relative position of the targetobject (n) is determined based on the lateral distance Dfy(n) and theinter-vehicle distance Dfx(n) of the detected target object (n). Thedriving support ECU 10 estimates a traveling direction of the ownvehicle based on the traveling speed SPD of the own vehicle and the yawrate YRt of the own vehicle. The following-target vehicle area is anarea previously determined such that, the longer the distance in thetraveling direction of the own vehicle becomes, the smaller the absolutevalue of the distance in the lateral direction with respect to thetraveling direction becomes. Then, when the relative position of thetarget object (n) is present within the following-target vehicle areafor a time equal to or longer than a predetermined time, the drivingsupport ECU 10 selects the target object (n) as the ACC-target vehicle.If a plurality of target objects (n) are present whose relativepositions are present within the following-target vehicle area for thetime equal to or longer than the predetermined time, the driving supportECU 10 selects as the ACC-target vehicle the target object having theminimum inter-vehicle distance Dfx(n) from among those target objects.

Further, the driving support ECU 10 calculates a target accelerationGtgt in accordance with any of the following Expressions (1) and (2). Inthe Expressions (1) and (2), Vfx(a) is a relative vehicle speed of theACC-target vehicle (a) with respect to the own vehicle, k1 and k2 arepredetermined positive gains or coefficients, and ΔD1 is aninter-vehicle distance difference obtained by subtracting a targetinter-vehicle distance Dtgt from the inter-vehicle distance Dfx(a) ofthe ACC-target vehicle (a) (ΔD1=Dfx(a)−Dtgt). The target inter-vehicledistance Dtgt is calculated by multiplying a target inter-vehicle timeTtgt by the vehicle speed SPD of the own vehicle 100 (Dtgt=Ttgt×SPD).The target inter-vehicle time Ttgt is set by the driver using theoperation switch 17.

The driving support ECU 10 determines the target acceleration Gtgt inaccordance with the following Expression (1) when the value (k1×ΔD1+k2×Vfx(a)) is positive or zero. In the Expression (1), ka1 is a positivegain or coefficient for accelerating the own vehicle and is set to avalue equal to or smaller than “1”.

Gtgt(for acceleration)=ka1×(k1×ΔD1+k2×Vfx(a))  (1)

On the other hand, when the value (k1× ΔD1+k2×Vfx(a)) is negative, thedriving support ECU 10 determines the target acceleration Gtgt inaccordance with the following Expression (2). In the Expression (2), kd1is a gain or coefficient for decelerating the own vehicle and in thisembodiment, is set to “1”.

Gtgt(for deceleration)=kd1×(k1×ΔD1+k2×Vfx(a))  (2)

When no target object is present within the following-target vehiclearea, the driving support ECU 10 determines the target acceleration Gtgtbased on the vehicle speed SPD of the own vehicle and a target vehiclespeed in such a manner that the vehicle speed SPD of the own vehiclematches up with (becomes equal to) the target vehicle speed which is setdepending on the target inter-vehicle time Ttgt.

The driving support ECU 10 controls the engine actuators 21 by using theengine ECU 20 and if necessary, and controls the brake actuator 31 byusing the brake ECU 30 in such a manner that the acceleration of the ownvehicle matches up with (becomes equal to) the target acceleration Gtgt.As described above, the driving support ECU 10 has, as a functional unitimplemented by the CPU, an “ACC control unit 10 a for performing thefollowing-travel inter-vehicle-distance control such as the ACC”.

<Lane Keeping Assist Control>

The driving support ECU 10 is configured to perform the lane keepingassist control when the lane keeping assist control is requested throughthe operation applied to the operation switch 17 while thefollowing-travel inter-vehicle-distance control (ACC) is beingperformed.

In the lane keeping assist control, the driving support ECU 10determines/sets/produces a target traveling line (target traveling path)by using one or both of the travel trajectory of the preceding vehicle(i.e., preceding vehicle trajectory) and the white lines. The targettraveling line is set within the lane in which the vehicle is currentlytraveling. The driving support ECU 10 applies the steering torque to thesteering mechanism to change the steering angle of the own vehicle insuch a manner that a lateral position of the own vehicle (i.e., aposition in the vehicle-width direction of the own vehicle with respectto the lane) is maintained in an immediate vicinity of (at a positionclose to) the target traveling line. In this manner, the steeringoperation of the driver can be assisted/supported. The lane keepingassist control is widely known (e.g., refer to Japanese PatentApplication Laid-open No. 2008-195402, Japanese Patent ApplicationLaid-open No. 2009-190464, Japanese Patent Application Laid-open No.2010-6279, and Japanese Patent No. 4349210). The lane keeping assistcontrol is also referred to as “Lane Trace Control (LTC)” or “TrafficJam Assist (TJA)”. Hereinafter, the lane keeping assist control will besometimes simply referred to as “LTC”.

Next, an aspect of the LTC will be described which is performed by usingthe target traveling line determined based on the preceding vehicletrajectory. The LTC according to this aspect is also referred to as the“follow-up steering control”. The preceding vehicle of which precedingvehicle trajectory is used to determine the target traveling line isalso referred to as a “follow-up preceding vehicle for steeringcontrol”. The driving support ECU 10 specifies/determines the precedingvehicle (that is, the follow-up preceding vehicle for steering control),which is the target object for obtaining/determining the precedingvehicle trajectory which is used to determine the target traveling line,in the same manner as when specifying the ACC-target vehicle.

As illustrated in FIG. 2, the driving support ECU 10specifies/determines the preceding vehicle 101 which is the targetobject for obtaining/determining the preceding vehicle trajectory L1.The driving support ECU 10 obtains/determines the preceding vehicletrajectory L1 based on the target object information. The target objectinformation includes information on positions of the preceding vehicle101 with respect to the position of the own vehicle 100 at predeterminedtime intervals. In the x-y coordinate shown in FIG. 2, the center axisextending in the front-rear direction of the own vehicle 100 is definedas the x-axis, the axis perpendicular to the x-axis is defined as they-axis, and the current position of the own vehicle 100 is defined asthe origin (x=0, y=0), respectively.

The symbols shown in FIG. 2 are as follows.

dv: a distance in the y-axis direction (substantially in the road-widthdirection) between the current position (x=0, y=0) of the centerposition in the vehicle-width direction of the own vehicle 100, and thepreceding vehicle trajectory L1. The distance dv is also referred to asa “deviation distance” for convenience.

θv: an angle of deviation (yaw angle) between the direction (tangentialdirection) of the preceding vehicle trajectory L1 at a positioncorresponding to the current position (x=0, y=0) of the own vehicle 100,and the traveling direction (“+” direction of the x-axis) of the ownvehicle 100.

Cv: a curvature of the preceding vehicle trajectory L1 at a position(x=0, y=dv) corresponding to the current position (x=0, y=0) of the ownvehicle 100.

Cv′: a change ratio of the curvature, that is, a curvature change amountper unit distance (Δx) at an any position (x=x0, x0 is an arbitraryvalue) of the preceding vehicle trajectory L1.

For example, the driving support ECU 10 stores (buffers) positioncoordinate data (position information) on the position of the precedingvehicle 101 in the RAM every time the certain sampling period of timeelapses. In order to minimize data to be stored in the RAM, the drivingsupport ECU 10 may store only a limited number of “relatively newposition coordinate data sets of the preceding vehicle 101” which havebeen obtained within a certain period up to the current time point andwhich includes the latest position coordinate data set, and discard theposition coordinate data sets older than the data sets obtained in thatcertain period. The driving support ECU 10 converts the positioncoordinate data of the preceding vehicle 101 stored in the RAM into theposition coordinate data of the above-described x-y coordinate systemwhere the current position of the own vehicle 100 is the origin (x=0,y=0). The driving support ECU 10 executes the above-mentioned convertingprocess based on the differences between (i) the position and travelingdirection of the own vehicle 100 at each time point at which theposition coordinate data is acquired, and (ii) the position andtraveling direction of the own vehicle 100 at the current time point. InFIG. 2, (x1, y1), (x2, y2), (x3, y3) and (x4, y4) are examples of theposition coordinate data of the preceding vehicle 101 which are obtainedby converting in the above-mentioned manner. Hereinafter, such positioncoordinate data are also referred to as “converted position coordinatedata”.

The driving support ECU 10 executes a curve fitting process by using theconverted position coordinate data of the preceding vehicle 101 toobtain the preceding vehicle trajectory L1 of the preceding vehicle 101.For example, a cubic function f(x) is used in the fitting curve process.In the fitting process, for example, the least squares method is used.As described above, the driving support ECU 10 has, as a functional unitimplemented by the CPU, a “travel trajectory obtaining unit 10 b forobtaining/extrapolating/determining the preceding vehicle trajectory L1which is the travel trajectory of the preceding vehicle”.

As illustrated in FIG. 3A, the preceding vehicle trajectory L1 isdefined by the following cubic function: f(x)=ax³+bx²+cx+d. Usingexpressions and conditions shown in FIG. 3B, the relationship shown inFIG. 3C, that is, the relationship between the coefficients (a, b, c andd) of the cubic function f(x), the curvature Cv, the yaw angle θv andthe like is derived. Therefore, the preceding vehicle trajectory L1 canbe expressed by the following Expression (3). As described above, thedriving support ECU 10 can determine/define the preceding vehicletrajectory L1 by obtaining the coefficients a, b, c and d of the cubicfunction f(x) by using the least squares method. Therefore, the changeratio of the curvature Cv′ of the preceding vehicle trajectory L1, thecurvature Cv of the preceding vehicle trajectory L1 at the positioncorresponding to the current position of the own vehicle 100, the yawangle θv at that position, and the distance dv at that position can beobtained.

f(x)=(⅙)Cv′×x ³+(½)Cv×x ² +θv×x+dv  (3)

When setting the preceding vehicle trajectory L1 as the target travelingline, the driving support ECU 10 acquires target lane informationnecessary for performing the follow-up steering control (one aspect ofthe LTC), based on the coefficients a, b, c and d of the cubic functionf(x), and the relationship shown in FIG. 3C. The target lane informationincludes the curvature Cv (and the change ratio of the curvature Cv′) ofthe target traveling line, the yaw angle θv of the own vehicle withrespect to the target traveling line, and the distance dv in theroad-width direction with respect to the target traveling line.

The driving support ECU 10 calculates, every time a predetermined periodof time elapses, a target steering angle θ* by applying the curvatureCv, the yaw angle θv and the distance dv to the following Expression(4). Further, the driving support ECU 10 controls the steering motor 42by using the steering ECU 40 in such a manner that an actual steeringangle θ of the own vehicle matches up with (becomes equal to) the targetsteering angle θ*.

In the Expression (4), Klta1, Klta2 and Klta3 are predetermined controlgains or coefficients.

θ*=Klta1×Cv+Klta2×θv+Klta3×dv  (4)

In addition, the above-mentioned target steering angle θ* is alsoreferred to as “target steering information” for convenience. The aboveis the outline of the follow-up steering control which is one aspect ofthe LTC performed by using the target traveling line determined based onthe preceding vehicle trajectory L1.

Next, an aspect of the LTC will be described which is performed by usingthe target traveling line determined based on the white lines. Asillustrated in FIG. 4, the driving support ECU 10 acquires informationon a left white line LL and a right white line LR of a travel lane inwhich the own vehicle 100 is currently traveling, based on theinformation transmitted from the ambient sensor 16 (i.e., theinformation which has been recognized by the camera sensor 16 b). Thedriving support ECU 10 extrapolates a line connecting center positionsin the road-width direction between the recognized pair of the whitelines LL and LR, and determines/defines the extrapolated line as acenter line LM of the travel lane. As described above, the drivingsupport ECU 10 has, as a functional unit implemented by the CPU, a “laneline recognition unit 10 c for extrapolating/determining the center lineLM which is the line connecting the center positions between therecognized pair of the white lines LL and LR”.

Further, the driving support ECU 10 calculates (i) a curve radius R anda curvature CL (=1/R) of the center line LM of the travel lane, and (ii)the position and the direction of the own vehicle 100 in the travel lanewhich is defined by the left white line LL and the right white line LR.Specifically, as illustrated in FIG. 4, the driving support ECU 10calculates (i) a distance dL in the y-axis direction (substantially inthe road-width direction) between the central position in thevehicle-width direction of the own vehicle 100 and the center line LM ofthe travel lane, and (ii) an angle of deviation 8L (yaw angle θL) formedbetween the direction (tangential direction) of the center line LM andthe traveling direction of the own vehicle 100. These parameters are thetarget lane information necessary for performing the LTC in the casewhere the center line LM of the travel lane is set as the targettraveling line. The target lane information includes the curvature CL ofthe target traveling line, the yaw angle θL of the own vehicle withrespect to the target traveling line, and the distance dL in theroad-width direction with respect to the target traveling line.

In the Expression (4), the driving support ECU 10 replaces dv, θv, andCv with dL, θL, and CL, respectively to thereby calculate the targetsteering angle θ*. The driving support ECU 10 controls the steeringmotor 42 by using the steering ECU 40 in such a manner that an actualsteering angle θ of the own vehicle matches up with (becomes equal to)the target steering angle θ*. Alternatively, the driving support ECU 10may control the steering motor 42 by using the Expression (4′).

The above is the outline of one aspect of the LTC performed by using thetarget traveling line determined based on the white lines.

Further, the driving support ECU 10 can determine/extrapolate/obtain thetarget traveling line based on the combination of the preceding vehicletrajectory L1 and the center line LM of the travel lane. Specifically,as illustrated in FIG. 5, the driving support ECU 10 corrects/modifiesthe preceding vehicle trajectory L1 in such a manner that the precedingvehicle trajectory L1 becomes a trajectory which has the shape(curvature) of the preceding vehicle trajectory L1, and which matches upwith the position and the direction (tangential direction) of the centerline LM in the vicinity of the own vehicle 100. This allows the drivingsupport ECU 10 to obtain, as the target traveling line, the precedingvehicle trajectory L2 which has the same shape (curvature) as thepreceding vehicle trajectory L1 and has a small offset/deviation in theroad-width direction with respect to the center line LM. Hereinafter,the preceding vehicle trajectory L2 which is obtained by correcting thepreceding vehicle trajectory L1 in the above manner will be referred toas a “corrected preceding vehicle trajectory L2”. The driving supportECU 10 acquires the target lane information when setting the correctedpreceding vehicle trajectory L2 as the target traveling line. Thedriving support ECU 10 calculates the target steering angle θ* based onthe target lane information and the above Expression (4). The drivingsupport ECU 10 controls the steering motor 42 in such a manner that anactual steering angle θ of the own vehicle matches up with (becomesequal to) the target steering angle θ*.

In accordance with the following situations (a) to (d), the drivingsupport ECU 10 of the embodiment apparatus sets the target travelingline in response to the presence/absence of the preceding vehicle andthe recognition state of the white lines, to perform the LTC.

(a) When the driving support ECU 10 has successfully recognized the leftand right white lines up to a far-away position (from the currentposition of the own vehicle to a position a first predetermined distanceaway), the driving support ECU 10 sets the target traveling line basedon the center line LM of the travel lane to thereby perform the LTC.

(b) When the follow-up preceding vehicle for steering control is presentahead of the own vehicle and the driving support ECU cannot recognizeany of the left and right white lines, the driving support ECU 10 setsthe target traveling line based on the preceding vehicle trajectory L1of the follow-up preceding vehicle for steering control to therebyperform the follow-up steering control which is one aspect of the LTC.

(c) When the follow-up preceding vehicle for steering control is presentahead of the own vehicle and the driving support ECU has recognized theleft and right white lines in the vicinity of the own vehicle (from thecurrent position of the own vehicle to a position a second predetermineddistance away, the second predetermined distance being shorter than thefirst predetermined distance), the driving support ECU 10 sets thetarget traveling line based on the corrected preceding vehicletrajectory L2 obtained by correcting the preceding vehicle trajectory L1of the follow-up preceding vehicle for steering control with the centerline LM of the recognized white lines to thereby perform the follow-upsteering control which is one aspect of the LTC.

(d) When no follow-up preceding vehicle for steering control is presentahead of the own vehicle and the driving support ECU cannot recognizethe left and right white lines up to a far-away position, the drivingsupport ECU 10 cancels the LTC.

As described above, the driving support ECU 10 has, as a functional unitimplemented by the CPU, a “LTC control unit (lane keeping assist controlunit) 10 d for performing the lane keeping assist control for changingthe steering angle of the own vehicle in such a manner that the ownvehicle travels along the target traveling line”.

<Outline of Operation>

In the above-mentioned situation (b), the driving support ECU 10 setsthe target traveling line based on the preceding vehicle trajectory L1of the follow-up preceding vehicle for steering control to perform thesteering control (i.e., the follow-up steering control) in such a mannerthat the own vehicle travels along the target traveling line. However,while the follow-up steering control is being performed, as illustratedin FIG. 6, if the preceding vehicle 101 travels at a position (near theleft edge 611 of the travel lane 610) away from the center line LM ofthe road (travel lane), the own vehicle 100 also travels near the leftedge 611 of the travel lane 610 owing to the follow-up steering control.

In the above-mentioned a situation, it is assumed that the driver wishesto modify the position of the own vehicle 100 to a position (100*) nearthe center line LM of the travel lane 610, and manually performs asteering operation (that is, manually operates the steering wheel SW).Owing to this steering operation, as illustrated by the arrow A in FIG.6, the position of the own vehicle 100 moves toward the center line LMin the road-width direction. However, as the driver stops the manualsteering operation, the above-mentioned related-art apparatus performsthe follow-up steering control based on the preceding vehicle trajectoryso as to return the own vehicle 100 to a position near the left edge 611of the travel lane 610 as illustrated by the arrow B. That is, while thefollow-up steering control is being performed, even if the driverintentionally performs the steering operation to modify the position ofthe own vehicle 100, there is a problem that the modified position ofthe own vehicle 100 cannot be maintained.

In order to solve the problem, in the above-mentioned situation (b), thedriving support ECU 10 of the embodiment apparatus is configured toswitch system states (in other words, control modes or control aspects)between a first state (first mode) and a second state (second mode) asdescribed below. The first state is a state in which it is permitted(allowed) to perform the follow-up steering control based on thepreceding vehicle trajectory L1. The second state is a state in whichthe follow-up steering control based on the preceding vehicle trajectoryL1 is stopped (prohibited). When a specific condition (hereinafter, alsoreferred to as a “predetermined control resumption condition”) issatisfied in the second state, the follow-up steering control isresumed/restarted. The driving support ECU 10 switches the system statesfrom the first state to the second state in response to the distancebetween the own vehicle 100 and the preceding vehicle trajectory L1, adetection result of the steering operation by the driver, and/or thelike (that is, when a “control stop condition” described later issatisfied).

In addition, the above-mentioned second state means that only theperformance of the follow-up steering control based on the precedingvehicle trajectory L1 is stopped (prohibited). In other words, in thesecond state, the performance of the LTC in the above-mentionedsituation (a) is not prevented. That is, when the driving support ECU 10has been recognizing the left and right white lines up to a relativelyfar distance from the current position of the own vehicle, the drivingsupport ECU 10 performs the LTC based on the center line LM which isextrapolated based on the recognized left and right white lines.

<Content of Processing>

Next, with reference to FIGS. 6 to 9, the “follow-up steering controlwhich is performed by the driving support ECU 10 when the driverperforms the steering operation” will be described. In the examplesillustrated in FIGS. 6 to 9, the driving support ECU 10 is performingthe ACC.

In the example shown in FIG. 6, the preceding vehicle (i.e., follow-uppreceding vehicle for steering control) 101 travels near the left edge611 in the travel lane 610. At time t=t1 which is a calculation timing,it is assumed that the camera sensor 16 b cannot recognize the leftwhite line and the right white line. Under this assumption, at time t1,the driving support ECU 10 sets the target traveling line based on thepreceding vehicle trajectory L1 of the preceding vehicle 101 to performthe follow-up steering control (that is, the current system state is thefirst state). Owing to the follow-up steering control, the own vehicle100 travels near the left edge 611 in the travel lane 610 so as tofollow the preceding vehicle trajectory L1. In such a situation, it isfurther assumed that the driver manually operates the steering wheel SW(that is, manually performs a steering operation) in such a manner thatthe position of the own vehicle 100 is modified/moved to the position(100*) near the center line LM of the travel lane 610.

A time after a predetermined time period (time period longer than theabove-mentioned sampling period of time) elapses from time t1 is denotedby t=t2. As illustrated in FIG. 7, at time t2, the own vehicle 100travels toward the center line LM of the travel lane 610 owing to thesteering operation of the driver.

On the other hand, every time the predetermined period of time elapses(every time the calculation timing arrives), the driving support ECU 10calculates the distance dv in the road-width direction between thecentral position in the vehicle-width direction of the own vehicle 100and the preceding vehicle trajectory L1. Further, every time thepredetermined period of time elapses, the driving support ECU 10determines whether or not the distance dv is equal to or longer than apredetermined first threshold Th1. When the distance dv is equal to orlonger than the first threshold Th1, a first distance condition issatisfied.

As illustrated in FIG. 7, when the distance dv is equal to or longerthan the first threshold Th1 (that is, the first distance condition issatisfied), the driving support ECU 10 determines whether or not apredetermined manual steering condition is satisfied. The manualsteering condition is satisfied when the driver operates the steeringwheel SW. When both of the first distance condition and the manualsteering condition are satisfied, the above-mentioned control stopcondition is satisfied.

For example, the manual steering condition is satisfied when thefollowing Expression (5) is satisfied. “θ” is an actual steering angledetected by the steering angle sensor 13 at time t. “θ*” is the targetsteering angle calculated based on the preceding vehicle trajectory L1obtained at time t. “Thθ” is a predetermined steering angle threshold(hereinafter, also referred to as a “third threshold” for convenience).

|θ−θ*|≥Thθ  (5)

As illustrated in FIG. 7, at time t2, in the situation in which thepreceding vehicle 101 travels near the left edge 611 of the travel lane610, the driver manually has operated the steering wheel SW in such amanner that the own vehicle 100 moves from left to right in theroad-width direction. The difference (|θ−θ*|) between the steering angleθ detected at the current time point (time t2) and the target steeringangle θ* calculated at the current time point is larger than thepredetermined steering angle threshold Thθ. Therefore, the manualsteering condition is satisfied. When the distance dv is equal to orlarger/longer than the first threshold Th1 and the manual steeringcondition is satisfied (that is, the control stop condition issatisfied), the driving support ECU 10 determines that the driverintentionally performs the manual steering operation to modify/changethe position of the own vehicle 100. When it is determined that thedriver intentionally has modified/changed the position of the ownvehicle 100, the driving support ECU 10 stops (halts/pause) thefollow-up steering control based on the preceding vehicle trajectory L1.Then, the driving support ECU 10 changes the system states from thefirst state to the second state. The second state is maintained untilthe predetermined control resumption condition described later issatisfied as long as a predetermined execution condition for thefollow-up steering control is satisfied.

According to the embodiment apparatus including the above-mentionedconfiguration, when the driver manually performs the steering operationto modify/change the position of the own vehicle 100, the follow-upsteering control based on the preceding vehicle trajectory L1 is notperformed. Therefore, the position of the own vehicle 100 is notreturned to the position near the left edge 611 of the travel lane 610.Accordingly, the position of the own vehicle 100 modified/changed by thedriver can be maintained.

On the other hand, when the distance dv is shorter than the firstthreshold Th1, the driving support ECU 10 performs the follow-upsteering control based on the preceding vehicle trajectory L1 (that is,the first state is maintained).

Further, even if the distance dv is equal to or longer than the firstthreshold Th1, when the manual steering condition is not satisfied, thedriving support ECU 10 performs the follow-up steering control based onthe preceding vehicle trajectory L1 (that is, the first state ismaintained).

In addition, even when the driver manually performs the steeringoperation, the manual steering condition is designed to be unsatisfiedunder the following (X) or (Y) state:

(X): A state where the driver manually performs an additional steeringoperation so as to bring the own vehicle 100 close to the precedingvehicle trajectory L1, when the position of the own vehicle 100 is awayfrom the preceding vehicle trajectory L1.

(Y): A state where the driver turns the steering wheel SW to the right(or left) as an additional steering operation in accordance with thetravel lane which curves to the right (or left).

In the case of (X) or (Y), since the driver turns the steering wheel SWin the same direction as the direction represented by the targetsteering angle θ, the above difference (|θ−θ*|) is smaller than thesteering angle threshold Thθ. Therefore, the manual steering conditionis not satisfied. When the driver performs an additional steeringoperation to bring the position of the own vehicle 100 close to thepreceding vehicle trajectory L1 or the driver performs an additionalsteering operation to have the own vehicle 100 travel safely in thecurved lane, the driving support ECU 10 continues performing thefollow-up steering control based on the preceding vehicle trajectory L1.That is, the first state is maintained.

Next, with reference to FIGS. 8 and 9, an operation after the systemstate is changed to the second state (that is, after the follow-upsteering control is stopped) will be described. As already describedwith reference to FIG. 7, since the first distance condition and themanual steering condition are both satisfied at time t2, the systemstate becomes the second state. After time t2, every time thepredetermined period of time elapses, the driving support ECU 10repeatedly obtains the preceding vehicle trajectory L1 based onnewly-obtained position coordinate data of the preceding vehicle 101,and determines whether or not the predetermined control resumptioncondition is satisfied. The control resumption condition is satisfiedwhen the distance dv is equal to or shorter than a predetermined secondthreshold Th2. This control resumption condition may be referred to as a“second distance condition”. The second threshold Th2 is set to a valueshorter than the first threshold Th1. While the control resumptioncondition is not satisfied (that is, the distance dv is longer than thesecond threshold Th2), even in the situation in which the follow-uppreceding vehicle for steering control is present ahead of the ownvehicle 100, the driving support ECU 10 maintains the second state anddoes not perform the follow-up steering control based on the precedingvehicle trajectory L1. Note, however, that the driving support ECU 10repeatedly selects the follow-up preceding vehicle for steering control,and continues obtaining the preceding vehicle trajectory L1 of theselected follow-up preceding vehicle for steering control.

A time after a certain time period elapses from time t2 is denoted bytime t=t3. As illustrated in FIG. 8, at time t3, the preceding vehicle101 is away from the left edge 611 of the travel lane 610 and istraveling in the vicinity of the center line LM of the travel lane 610.For this reason, at time t3, the distance dv becomes equal to or shorterthan the predetermined second threshold Th2. Therefore, the controlresumption condition is satisfied. The driving support ECU 10 changesthe system states from the second state to the first state to resume thefollow-up steering control based on the preceding vehicle trajectory L1.

As another example, as illustrated in FIG. 9, it is assumed that, attime t=t3′ after a certain time period elapses from time t2, the drivermanually performs the steering operation to bring the own vehicle 100close to a position near the left edge 611 of the travel lane 610. Inthis case, since the driver intentionally brings the position of the ownvehicle 100 close to the preceding vehicle trajectory L1 of thepreceding vehicle 101, it is desirable to have the own vehicle 100follow the preceding vehicle trajectory L1 of the preceding vehicle 101in view of the intention of the driver. In this case as well, since thedistance dv becomes equal to or shorter than the second threshold Th2,the control resumption condition is satisfied. Therefore, the drivingsupport ECU 10 changes the system states from the second state to thefirst state to resume the follow-up steering control based on thepreceding vehicle trajectory L1.

In the above-mentioned manner, when the control resumption conditionbecomes satisfied (that is, the distance dv becomes equal to or shorterthan the predetermined second threshold Th2) after the system state hasbeen changed to the second state, the driving support ECU 10 resumes thefollow-up steering control based on the preceding vehicle trajectory L1.Therefore, the embodiment apparatus can have the own vehicle 100 followthe preceding vehicle trajectory L1 of the preceding vehicle 101 even ifthe driver does not perform a specific operation (i.e., withoutrequiring the driver to perform a specific operation).

In order to perform the above-mentioned control, the driving support ECU10 manages a state flag F. When the state flag F is “0”, this means thatthe current system state is the first state. When the state flag F is“1”, this means that the current system state is the second state.

<Concrete Operation>

Next, a concrete operation of the CPU (hereinafter, simply referred toas the “CPU”) of the driving support ECU 10 will be described. As oneroutine for performing the LTC, the CPU is configured or programmed toexecute a routine shown by a flowchart in FIG. 10, every time thepredetermined period of time elapses (that is, every time thepredetermined calculation timing arrives). In addition, the CPU executesthe routine of FIG. 10 while the ACC is being performed.

Therefore, in the case where the ACC is being performed, as thepredetermined calculation timing arrives, the CPU starts from a processof Step 1000 in FIG. 10, and proceeds to Step 1005 to determine whetheror not a predetermined execution condition is satisfied. Thepredetermined execution condition is also referred to as an “executioncondition for the follow-up steering control”.

The predetermined execution condition is satisfied when the followingconditions 1 and 2 are both satisfied.

(condition 1): The execution of the LTC is being selected through theoperation of the operation switch 17.

(condition 2): Up to the current calculation timing, the camera sensor16 b has not recognized the left white line and the right white line forsetting the center line LM of the travel lane to sufficiently fardistance. That is, the CPU is not performing the LTC based on the centerline LM of the travel lane at the current time point.

When the predetermined execution condition is not satisfied, the CPUmakes a “No” determination at Step 1005, and proceeds directly to Step1095 to tentatively terminate the present routine. In this case, thefollow-up steering control based on the preceding vehicle trajectory L1is not performed.

On the other hand, when the predetermined execution condition issatisfied, the CPU makes a “Yes” determination at Step 1005, andproceeds to Step 1010 to determine whether or not a preceding vehicle ispresent in a front area of (ahead of) the own vehicle 100.

When no other vehicle is present in the front area of the own vehicle100, the CPU makes a “No” determination at Step 1010, and proceedsdirectly to Step 1095 to tentatively terminate the present routine.

It is assumed that an other vehicle is newly detected in the front areaof the own vehicle 100 at the current time point. In this case, the CPUmakes a “Yes” determination at Step 1010, and proceeds to Step 1015.

At Step 1015, the CPU acquires the traveling speed SPD of the ownvehicle 100 from the vehicle speed sensor 15, and the yaw rate of theown vehicle 100 from the yaw rate sensor 18. Further, the CPUextrapolates the traveling direction of the own vehicle 100 based on theacquired traveling speed SPD and yaw rate. The CPU selects, as thefollow-up preceding vehicle for steering control, the nearest targetobject from the own vehicle 100 in its traveling direction, based on thetarget object information transmitted from the ambient sensor 16.Hereinafter, the follow-up preceding vehicle for steering control issimply referred to as the “preceding vehicle”. Although not shown inFIG. 10, if the preceding vehicle cannot be selected, the CPU proceedsdirectly to Step 1095 from Step 1015 to tentatively terminate thepresent routine. In this case, the follow-up steering control based onthe preceding vehicle trajectory L1 is not performed.

Next, the CPU proceeds to Step 1020 to determine whether or not a flagreset condition is satisfied. For example, the flag reset condition issatisfied when at least one of the following conditions 3 and 4 issatisfied.

(condition 3): Although the CPU did not select the preceding vehicle atthe previous calculation timing, the CPU newly selects the precedingvehicle at the current calculation timing.

(condition 4): The preceding vehicle selected at the current calculationtiming is different from a vehicle selected as the preceding vehicleselected at the previous calculation timing.

If the preceding vehicle is newly selected at the current calculationtiming, the above-mentioned condition 3 is satisfied, and thus, the flagreset condition is also satisfied. Therefore, the CPU makes a “Yes”determination at Step 1020, and proceeds to Step 1025. The CPU sets thevalue of the state flag F to “0” at Step 1025, and proceeds to Step1030.

As described above, the CPU stores the position coordinate data for eachtarget object in the RAM in association with each target object, basedon the target object information from the ambient sensor 16. At Step1030, the CPU acquires the position coordinate data corresponding to thepreceding vehicle selected at Step 1015 from among the pieces of theposition coordinate data. The CPU calculates the converted positioncoordinate data based on the acquired position coordinate data. Further,the CPU executes the curve fitting process with respect to the convertedposition coordinate data to obtain the preceding vehicle trajectory L1of the preceding vehicle.

Next, the CPU proceeds to Step 1035, and calculates the target steeringangle θ* as the target steering information using the Expression (4) asdescribed above.

Next, at Step 1040, the CPU determines whether or not the state flag Fis “0”. Since the state flag F is now “0”, the CPU makes a “Yes”determination, and proceeds to Step 1045.

Next, at Step 1045, the CPU determines whether or not the distance dv isequal to or longer than the first threshold Th1. That is, the CPUdetermines whether or not the first distance condition is satisfied. Itis assumed that the position of the own vehicle 100 is close to thepreceding vehicle trajectory L1, and therefore, the distance dv isshorter than the first threshold Th1. In this case, the CPU makes a “No”determination at Step 1045, and proceeds to Step 1070. As describedlater, at Step 1070, the follow-up steering control based on thepreceding vehicle trajectory L1 is performed.

On the other hand, it is assumed that the position of the own vehicle100 is away from the preceding vehicle trajectory L1, and therefore, thedistance dv is equal to or longer than the first threshold Th1. In thiscase, since the first distance condition is satisfied, the CPU makes a“Yes” determination at Step 1045, and proceeds to Step 1050. At Step1050, the CPU acquires information on the steering angle θ at thecurrent time point from the steering angle sensor 13, and determineswhether or not the predetermined manual steering condition (i.e.,Expression (5)) is satisfied based on the steering angle θ and thetarget steering angle θ* calculated at Step 1035. Here, it is assumedthat the driver is not performing the steering operation. In this case,since the manual steering condition is not satisfied, the CPU makes a“No” determination at Step 1050, and proceeds to Step 1070.

When the CPU proceeds to Step 1070, the CPU performs the follow-upsteering control based on the preceding vehicle trajectory L1. That is,the CPU performs the steering control in such a manner that the steeringangle θ at the current time point matches up with (becomes equal to) thetarget steering angle θ*. Then, the CPU proceeds to Step 1095 totentatively terminate the present routine.

Here, after the predetermined period of time elapses in the abovesituation, it is assumed that the driver has performed the steeringoperation manually so that the situation described with reference toFIG. 7 has occurred. In this case, as the predetermined calculationtiming arrives, the CPU resumes the process from Step 1000. When the CPUproceeds to Step 1005, the above-mentioned predetermined executioncondition (all of the conditions 1 and 2) is again satisfied. Therefore,the CPU proceeds from Step 1005 to Step 1010. Further, the precedingvehicle is present ahead of the own vehicle 100 in this situation.Therefore, the CPU proceeds from Step 1010 to Step 1015, and selectsagain that preceding vehicle. Thereafter, the CPU proceeds to Step 1020.

In this case, the preceding vehicle has been selected at the previouscalculation timing, and the preceding vehicle selected at the currentcalculation timing is the same as a vehicle selected as the precedingvehicle selected at the previous calculation timing. Therefore, neitherof the above-mentioned condition 3 nor condition 4 is satisfied. Thatis, the flag reset condition is not satisfied. Therefore, the CPU makesa “No” determination at Step 1020 and proceeds directly to Step 1030. Asa result, the value of the state flag F is maintained at “0”.

The CPU again obtains the preceding vehicle trajectory L1 of thepreceding vehicle at Step 1030, and proceeds to Step 1035 to calculatethe target steering angle θ*.

Next, at Step 1040, the CPU determines whether or not the state flag Fis “0”. Since the state flag F is now “0”, the CPU makes a “Yes”determination, and proceeds to Step 1045.

Next, at Step 1045, the CPU determines whether or not the distance dv isequal to or longer than the first threshold Th1. Since the situation asdescribed with reference to FIG. 7 occurs at present, the distance dv isequal to or longer than the first threshold Th1. That is, the firstdistance condition is satisfied. Therefore, the CPU makes a “Yes”determination at Step 1045, and proceeds to Step 1050 to determinewhether or not the above-mentioned manual steering condition issatisfied.

Since the manual steering condition is now satisfied, the CPU makes a“Yes” determination at Step 1050, and proceeds to Step 1055 to set thevalue of the state flag F to “1”. That is, the system state is changedfrom the first state to the second state. That is, the CPU does notperform the follow-up steering control based on the preceding vehicletrajectory L1, and proceeds to Step 1095 to tentatively terminate thepresent routine.

After the predetermined period of time elapses in this situation, theCPU resumes the process from Step 1000. When the CPU proceeds to Step1005, the above-mentioned predetermined execution condition (all of theconditions 1 and 2) is again satisfied. Therefore, the CPU proceeds fromStep 1005 to Step 1010. Further, the preceding vehicle is present aheadof the own vehicle 100 in this situation. Therefore, the CPU proceedsfrom Step 1010 to Step 1015, and selects again that preceding vehicle.Thereafter, the CPU proceeds to Step 1020.

In this situation, neither of the above-mentioned condition 3 norcondition 4 is satisfied. That is, the flag reset condition is notsatisfied. Therefore, the CPU makes a “No” determination at Step 1020,and proceed directly to Step 1030. As a result, the state flag F ismaintained at “1”.

The CPU again obtains the preceding vehicle trajectory L1 of thepreceding vehicle at Step 1030, and calculates the target steering angleθ* at Step 1035.

Next, at Step 1040, the CPU determines whether or not the state flag Fis “0”. Since the state flag F is now “1”, the CPU makes a “No”determination and proceeds to Step 1060.

At Step 1060, the CPU determines whether or not the above-mentionedcontrol resumption condition is satisfied. Here, it is assumed that theposition of the preceding vehicle 101 has been changed during a timeperiod from the previous calculation timing to the current calculationtiming, and therefore, the situation as described with reference to FG.8 has occurred. In this case, since the distance dv is equal to orshorter than the second threshold Th2, the control resumption conditionis satisfied. Therefore, the CPU makes a “Yes” determination at Step1060, and proceeds to Step 1065 to set the value of the state flag F to“0”. That is, the system state is changed from the second state to thefirst state. Thereafter, the CPU proceeds to Step 1070 to resume thefollow-up steering control based on the preceding vehicle trajectory L1.Next, the CPU proceeds to Step 1095 to tentatively terminate the presentroutine.

It should be noted that, at the time point at which the CPU executes theprocess of Step 1060, in a case where the driver has manually performedthe steering operation to bring the own vehicle 100 to a position closeto the preceding vehicle trajectory L1 as described with reference toFIG. 9, the control resumption condition is also satisfied. In thiscase, the CPU proceeds to Step 1070 via Step 1065 to resume thefollow-up steering control based on the preceding vehicle trajectory L1.

On the other hand, it is assumed that, when the CPU proceeds to Step1060, the preceding vehicle 101 still travels near the left edge 611 ofthe travel lane 610. In this case, the CPU makes a “No” determination atStep 1060, and proceeds to Step 1095 to tentatively terminate thepresent routine. Therefore, the value of the state flag F is maintainedat “1”. That is, the CPU maintains the system state at the second state,and therefore, does not perform the follow-up steering control based onthe preceding vehicle trajectory L1.

As described above, when the first distance condition is satisfied andthe manual steering condition is satisfied while the follow-up steeringcontrol based on the preceding vehicle trajectory L1 is being performed,the embodiment apparatus does not perform (stops) the follow-up steeringcontrol based on the preceding vehicle trajectory L1, and changes thesystem states from the first state to the second state. Therefore, whenthe driver intentionally and manually performs the steering operation tomodify the position of the own vehicle 100 as described above withreference to FIG. 7, the position of the own vehicle 100 is not returnedto the “position before that modification”, because the follow-upsteering control based on the preceding vehicle trajectory L1 is notperformed. Thus, the embodiment apparatus can maintain the position ofthe own vehicle 100 which is modified by the driver during performanceof the follow-up steering control.

Further, after the system state once becomes the second state, theembodiment apparatus maintains the second state while (as long as) thedistance dv is longer than the second threshold value Th2. Meanwhile,when the distance dv becomes equal to or shorter than the secondthreshold Th2 (that is, the control resumption condition becomessatisfied), the embodiment apparatus resumes the follow-up steeringcontrol based on the preceding vehicle trajectory L1. Therefore, even ifthe system state becomes the second state, when the preceding vehicle101 is moved to a position in the vicinity of the center line LM of thetravel lane 610 (refer to FIG. 8) or when the driver intentionally movesthe own vehicle 100 to a position in the vicinity of the precedingvehicle trajectory L1 (refer to FIG. 9), and the like, the embodimentapparatus resumes the follow-up steering control based on the precedingvehicle trajectory L1. In this manner, the embodiment apparatusautomatically resumes the follow-up steering control based on thepreceding vehicle trajectory L1 in response to the positionalrelationship between the own vehicle 100 and the preceding vehicle 101,even if the driver does not perform a specific operation (that is,without requiring the driver to perform a specific/particularoperation).

The present disclosure is not limited to the above-mentioned embodiment,and various changes can be adopted within the scope of the presentdisclosure.

For example, at Step 1030, the CPU may obtain/calculate/produce thepreceding vehicle trajectory L1 by using the Kalman filter. Morespecifically, in some embodiments, the driving support ECU 10 includesthe Kalman filter. The CPU inputs/applies, to the Kalman filter, theposition information of the own vehicle and the position information ofthe follow-up preceding vehicle for steering control which has beenstored in the RAM. In response to this input, the Kalman filter outputs(i) the curvature Cv of the preceding vehicle trajectory L1 at aposition corresponding to the current position of the own vehicle 100,(ii) the change ratio of the curvature Cv′ of the preceding vehicletrajectory L1, (iii) the yaw angle θv of the own vehicle 100 withrespect to the preceding vehicle trajectory L1, and (iv) the distance dvbetween the current position of the own vehicle 100 and the precedingvehicle trajectory L1. The CPU can obtain the coefficients a, b, c, andd of the cubic function f(x) based on the relationship shown in FIG. 3C(that is, the relationship between/among the coefficients (a, b, c, andd) of the cubic function f(x), the curvature, the yaw angle and thelike).

In some embodiments, when the CPU has recognized the white lines in thevicinity of the own vehicle 100 before the time point at which the CPUexecutes the process of Step 1030, the CPU obtains/calculates thecorrected preceding vehicle trajectory L2 through correcting/modifyingthe preceding vehicle trajectory L1 with the recognized white lines.

In some embodiments, the CPU may use the steering torque Tra as thesteering-related amount at Step 1050. In this configuration, the manualsteering condition may be the following Expression (5′). “Tra” is asteering torque detected by the steering torque sensor 14 at time t.“Thr” is a predetermined torque threshold (also referred to as a “fourththreshold” for convenience).

|Tra|≥Thr  (5′)

The embodiment apparatus is configured to perform the LTC only while theACC is being performed. However, the embodiment apparatus may beconfigured to perform the LTC even while the ACC is not being performed.

What is claimed is:
 1. A driving support apparatus for a vehiclecomprising: a steering operation unit configured to be operated by adriver of the vehicle; a steering device configured to change a steeringangle of the vehicle in response to an operation amount of the steeringoperation unit; a travel trajectory obtaining unit configured to obtaina preceding vehicle trajectory which is a travel trajectory of apreceding vehicle traveling ahead of the vehicle; and a control unitconfigured to perform a follow-up steering control for changing thesteering angle of the vehicle in such a manner that the vehicle travelsalong a target traveling line determined based on the preceding vehicletrajectory, the control unit being configured to, when a first distancecondition and a manual steering condition are both satisfied while thefollow-up steering control is being performed, stop the follow-upsteering control, the first distance condition being a conditionsatisfied when a deviation distance in a road-width direction betweenthe preceding vehicle trajectory and the vehicle is equal to or longerthan a predetermined first threshold, and the manual steering conditionbeing a condition satisfied when the driver operates the steeringoperation unit to change a position in the road-width direction of thevehicle.
 2. The driving support apparatus according to claim 1, whereinthe control unit is configured to, when a second distance condition issatisfied in a state in which the follow-up steering control is stoppedowing to the satisfaction of both the first distance condition and themanual steering condition, resume the follow-up steering control, thesecond distance condition being a condition satisfied when the deviationdistance is equal to or shorter than a predetermined second threshold.3. The driving support apparatus according to claim 1, furthercomprising a detector configured to detect a steering-related amountwhich is an amount concerning an operation state of the steeringoperation unit, wherein the control unit is configured to determinewhether or not the manual steering condition is satisfied based on thedetected steering-related amount.
 4. The driving support apparatusaccording to claim 2, further comprising a detector configured to detecta steering-related amount which is an amount concerning an operationstate of the steering operation unit, wherein the control unit isconfigured to determine whether or not the manual steering condition issatisfied based on the detected steering-related amount.